In recent years, From the viewpoint of space saving, in place of a CRT type display conventionally and widely used, there have been widely used, flat panel displays such as a liquid crystal display, a plasma display, an OLED display, and a field emission display. Further reduction in thickness is demanded for these flat panel displays. In particular, it is required that the OLED display be easily carried by being folded or wound and be usable not only on a flat surface but also on a curved surface. Further, it is not just displays that are required to be usable not only on a flat surface but also on a curved surface. For example, if a solar cell or an OLED lighting device can be formed on a surface of an object having a curved surface, such as a surface of an automobile body, or a roof, a pillar, or an outer wall of a building, the applications of the solar cell or OLED lighting device may expand. Substrates and cover glasses used for these devices are required to be a thinner sheet and to have high flexibility.
A light-emitting element used for an OLED display deteriorates in quality through the contact of gasses such as oxygen and water vapor. Thus, a substrate used for the OLED display is required to have high gas-barrier property, and hence the use of a glass substrate for the substrate is expected. However, glass used for a substrate is weak in tensile stress unlike a resin film, and hence is low in flexibility. Thus, concentrarion of a tensile stress on a surface of a glass substrate by bending the glass substrate leads to the breakage of the glass substrate. In order to impart flexibility to the glass substrate, the glass substrate is required to achieve an ultra thin sheet. Thus, a glass film having a thickness of 200 μm or less is proposed as described in Patent Document 1 below.
A glass substrate used for electronic devices such as a flat panel display and a solar cell is subjected to various treatments associated with electronic device production, such as a treatment for providing a film such as a transparent conductive film and a cleaning treatment. However, when a glass film is used as a glass substrate for these electronic devices, the glass film breaks due to a stress change even at a small amount, because glass is a brittle material. Thus, there is a problem in that the handling of the glass film is very difficult, when the above-mentioned various treatments associated with electronic device production are carried out. In addition, there is another problem in that a glass film having a thickness of 200 μm or less is rich in flexibility, and hence the positioning of the glass film is difficult when the treatments associated with production are carried out, so that displacement or the like in patterning may occur.
Therefore, in order to enhance a handling easiness of a glass film, proposed is a laminate in which a glass film is laminated on a resin film after a pressure-sensitive adhesive substance is coated on the resin film. In such the glass film laminate, the glass film is supported by the resin film being a tough material, and hence the handling of the glass film laminate becomes easier compared to a case of the glass film alone when the above-mentioned various treatments associated with production are carried out.
However, there is a problem in that when the resin film is finally peeled off from the laminate to provide a glass film solely, the glass film which is a brittle material is easy to break, and the pressure-sensitive adhesive substance remains on the glass film after the resin film is peeled off, causing contamination. Further, there is a difference in thermal expansion coefficients of the resin film and the glass film, and hence, even in a case where a heat treatment is carried out at a relatively low temperature of around 200° C. as a treatment associated with production, there is a possibility in that thermal warpage, resin peeling, or the like may occur. In addition, there is another problem in that displacement or the like easily occurs when the positioning and the patterning during treatments associated with production are carried out, because the resin film is also rich in flexibility.
In order to solve the above-mentioned problems, a laminate is proposed as described in Patent Document 2 below. Patent Document 2 below proposes a laminate in which a supporting glass and a glass sheet are laminated via a pressure-sensitive adhesive layer that may be maintained almost stably even after its repeated use. According to such the laminate, even if a glass sheet having less strength and rigidity by itself is used, the production of a liquid crystal display device may be carried out with sharing a conventional line for producing a liquid crystal display device. Thus, after completion of the production processes, peeling off the glass sheet can be carried out quickly without the breakage of the glass substrate. Further, the thermal warpage or the like can be prevented from occurring to some extent, because the supporting member is made of glass. In addition, displacement or the like hardly occurs when the positioning and patterning during treatments associated with production are carried out, because the support member has high rigidity.
However, even in the above-mentioned laminate, there has not yet been solved such a problem that a pressure-sensitive adhesive remains on the thin glass sheet after peeling off of the supporting glass.